I agree that we should not make up our own procedures by switching major systems on or off unless directed to; people have killed themselves by doing that.
The youtube link does not work, and I don’t have current access to details of a DC Ess Bus failure, however, if only ACP2 works, but the F/O has to fly, would the F/O’s headset lead reach over to the LHS? - (routing behind the F/O - I can’t try this myself at the moment). If so the Cap could wear the F/O’s headset and key the F/O boom mic via the PTT switch on ACP2, which is easy to reach.
Leaving the speaker(s) on as well would keep the F/O in the loop.